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40 Cards in this Set
- Front
- Back
What does SPECT stand for?
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single photon emission computed tomography
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What is the benefit of multidetector camera setup over single detector SPECT?
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Faster: They acquire data simultaneously from multiple directions.
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Components of Anger Camera
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...
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During Cardiac imaging the SPECT camera is configured in an (L, H) configuration and undergoes a rotation arc of _______ degrees
How about non-cardiac imaging? |
L position
180 degrees (better spatial resolution but more noisy) H position 360 degrees (less spatial resolution but more homogeneous) |
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Most Tc-99m clinical protocols use how many projections over 180 degrees with high resolution collimators?
over 360 degrees? |
64 projections/180 degrees
128 projections/360 degrees |
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Which type of orbit provides the best signal characteristics, circular or non-circular orbit?
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non-circular: because the camera remains close to the patient throughout image acquisition resulting in better spatial resolution and signal
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Which type of SPECT detector is best? Anger cameras or solid state cameras
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solid state cameras:
better resolution, better sensitivity, requires less radiopharmaceutical, faster, lower dose to patient |
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Attenuation correction can be done simply by acquiring images in 180 degree projections and then averaging the information. This is known as what?
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Geometric Mean
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How does the energy of the gamma ray emitted by the isotope relate to attenuation?
how about the size of the patient? |
lower energy = higher attenuation in patient
fat patient= more attenuation |
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What clinical application is a chang attenuation correction applied?
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for attenuation correction of cylindrical bodies (ie. brain imaging)
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How does emission/transmission attenuation correction work?
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a line source emits radiation of different keV behind patient and attenuation is calculated based on the amount of radiation "transmitted" through the patient. This is then used to correct for the energy "emitted" from within the patient. This is done for both detectors for every projection throughout the arc.
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What are the pros and cons of CT attenuation correction?
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pros: better signal to noise ratio with a lower patient radiation dose.
cons: cannot be performed simultaneously with the emmision tomograms= misregistration. |
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Once the data of a SPECT image has been acquired, how is the image reconstructed?
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Filtered back projection
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What is the star artifact?
How is it reduced? |
Star artifact results from filtered back projection when too few projections are used
Use more projections |
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What are the effects of applying filters to the back projection?
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lower cutoff frequency = less noise at expense of spatial resolution
high cutoff frequency = more noise but better spatial resolution |
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Iterative reconstruction, MLEM and OSEM?
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just know that iterative reconstruction is better than filtered back projection
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How is the resolution of a SPECT system defined?
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FWHM (full width half max)
typically 1 cm |
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QC: How frequently are the following performed?
Energy Peaking Intrinsic floods Attenuation peaking and flood |
Daily
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QC: How frequently are the following performed?
Attenuation correction high-count maps |
Weekly
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QC: How frequently are the following performed?
High count extrinsic floods how will a nonuniform detector response look? |
weekly-monthly
concentric rings |
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QC: How frequently are the following performed?
Multipuspose plexiglas phantoms Tomographic resolution (line source/point source) 3D testing |
quarterly
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What is COR calibration? how frequently should it be done?
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Weekly: Provides information to the reconstruction software about the way the images appear to shift as the camera rotates around the body for different collimators. If not properly calibrated, can result in significant reconstruction artifacts
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In a multidetector SPECT system, the percent variation between detectors should not exceed what value?
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10%
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What are the predictable and variable SPECT artifacts?
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Predictable:
1) COR = comet 2) Tilt = Mercedes-Benz 3) Wrong Energy = Fuzzy Variable 1) Motion 2) Bad PM tube 3) Gating Errors |
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Name this artifact
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Uncalibrated COR= comet artifact
Anterolateral and inferolateral defects |
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Name this artifact
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Detector Tilt (>10 degrees) = mercedes benz
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Name this artifact
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Wrong energy peak = Fuzzy
Results in decreased count, spatial resolution and contrast |
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Remember motion and motion-like artifacts
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can be seen during cines if patient moves and when dual head cameras are used as the information from 2 cameras is combined (ie. apparent increased parathyroid uptake at the end of a 180 degree acquisition)
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what are causes of concentric ring artifacts?
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Damaged collimators, faulty PM tube, inadequate counts of a correcting flood field and nonuniform detector response.
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What is this artifact?
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Magnetic field effects
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What is this artifact?
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Ringing artifact: occurs when bright uptake in an organ results in decreased apparent signal in adjacent "less-hot" organ. Like shining or mach band
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For SPECT CT, how frequently should a phangom be used to verify correct registration between CT and SPECT?
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Quarterly
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What is the most common type of scintillation crystal?
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NaI (Tl)
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Non-circular paths equals better _____________
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spatial resolution.
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Cardiac imaging angles
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-45 to +135 degrees
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Chang correction is for uniform attenuation coefficients along with uniform radioactivity concentrations
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...
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The function that convolutes or blurs each point has the particular form of 1/r
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fixed by ramp function
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at the same distance, planar images and SPECT have ___________ resolution?
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Same
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COR artifact results in Anterolateral and inverolateral defects
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...
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CT Attenuation correction calibration should be performed ____________
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daily
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